Measurement device and support for use in a well

ABSTRACT

The invention provides a support for measurement means for monitoring and/or studying a fluid reservoir ( 13 ) through which at least one well ( 11 ) passes, said support comprising: a cylindrical tube ( 2 ); and a jacket ( 3 ) surrounding said cylindrical tube. According to the invention, said jacket ( 3 ) has at least one recess ( 4, 5 ) for receiving means ( 6 ) for measuring a characteristic representative of said reservoir and/or connection means ( 7 ) leading to power supply and measurement-processing means ( 16 ). The invention also provides a measurement device for monitoring and/or studying a fluid reservoir ( 13 ) through which at least one well ( 11 ) passes, said device comprising: power supply and measurement processing means ( 16 ); means ( 6 ) for measuring a characteristic representative of said reservoir, and connection means ( 7 ) connecting said measurement means ( 6 ) to said power supply and measurement processing means ( 16 ). According to the invention, said device ( 10 ) being characterized in that it further comprises at least one support ( 1 ) according to any preceding claim, with said measurement means ( 6 ) and said connection means ( 7 ) being housed in the recesses ( 4, 5 ) in the jacket ( 3 ) of said support.

[0001] The invention relates to a support for measurement means, andmore particularly to a support for measurement means for monitoringand/or studying a fluid reservoir having at least one well bored ingeological formations passing therethrough.

[0002] The production of hydrocarbons needs to be controlled andmonitored on a regular or permanent basis in order to determined thecauses of any stoppage or reduction in production and in order toattempt to provide a remedy. Apart from the production means in place,production also depends on the characteristics of the geologicalformations (porosity, permeability, . . . ) and of the fluids theycontain (water, oils, gas). In this respect, an important piece ofinformation is the positions within the reservoir of the contact surfacebetween hydrocarbons and water and between hydrocarbons and gas. It isessential not only to determine the levels of these contact surfaceswhen the well is put into place, but also at all times to know theircurrent positions and movements so as to avoid water or gas reaching theproduction zone.

[0003] In conventional manner, the resistivity of terrain is used as acharacteristic representative of the reservoir. The resistivity ofhydrocarbons is generally much greater than the resistivity of water ina formation since such water carries a load of salt (the resistivityratio is about 1 to 100). Document FR 2 712 627 describes a deviceenabling continuous measurement to be performed relating to a reservoirwithout affecting production, using means for measuring the potentialdifference between a measurement electrode fixed in the well and areference electrode. That device presents, amongst other things, casingfitted to a production well and carrying electrodes on its outside wall,which electrodes are connected via contact pieces and wiring toelectronic means also fixed on the outside of the casing. An electricalconnection cable connected to a current source serves to connect theelectronic means to the surface and runs along the casing. Cement isinjected into the annular gap between the outside wall of the casing andthe wall of the well so as to fix the device permanently in place,thereby making it possible to perform measurements without disturbingproduction.

[0004] Although it is very ingenious, that device presents variousdrawbacks coming mainly from the fact that the electrodes, theelectronic means, and the electrical connection means are all installedon the outside of the casing. That disposition gives rise firstly to allof those elements running the risk of being damaged while they are beinglowered down the well. The walls of wells are not accurately rectilinearand instruments for lowering items down a well are not always extremelyaccurate, so it can happen that the casing bangs into the wall. Undersuch circumstances, it is the more fragile devices, particularly theelectrodes and the electronic means that are subjected to impact andthat therefore run the risk of being seriously damaged or even madecompletely inoperative, which requires the casing to be raised back tothe surface and the defective element to be replaced, where such anoperation is lengthy and expensive.

[0005] Furthermore, that prior art device raises problems with cementingthe casing to the walls of the well. Discontinuities in the outsideprofile of the casing as caused by the presence of the electrodes, theelectronic means, and the connection wiring constitute risks ofobtaining cementing in the annulus between the wall of the well and thewall of the device that is discontinuous. This leads to fluids from therock formation infiltrating between the cemented annulus and the casing,thus damaging the casing and the measurement devices. Suchdiscontinuities can also lead to a path being formed enabling suchfluids to rise towards the surface, thereby not only damaging theequipment, but also endangering personnel in the vicinity of the well.

[0006] An object of the invention is thus to remedy those drawbacks byproposing a support for measurement means that is suitable forinstalling permanently in a well passing through a fluid reservoir whileavoiding damage to said means and deficiencies in the cemented annulus.

[0007] To this end, the invention provides a support for measurementmeans for monitoring and/or studying a fluid reservoir through which atleast one well passes, said support comprising:

[0008] a cylindrical tube; and

[0009] a jacket surrounding said cylindrical tube.

[0010] According to the invention, said jacket has at least one recessfor receiving means for measuring a characteristic representative ofsaid reservoir and/or connection means leading to power supply andmeasurement-processing means.

[0011] In this manner, the support of the invention enables measurementmeans, electronic means, and connection means to be lowered down thewell without said means projecting from the outside surface of thesupport as a whole. By housing these elements in recesses of a jacketthey are protected from impacts while the support is being lowered downthe well. Thereafter, the support of the invention possesses theadvantage of presenting an outside surface that is substantiallyuniform, i.e. without projections, such that cementing can be performeduniformly in the annulus between said support and the walls of the well,thus avoiding all of the above-mentioned drawbacks.

[0012] In a preferred embodiment of the invention, the jacket is made ofan electrically insulating material and the support includes a pluralityof recesses that are regularly spaced apart to receive respectivemeasurement means made of electrically conductive material.Advantageously, the measurement means comprise at least one measurementelectrode, an electrode for injecting current into the reservoir and/ora current return electrode, thereby enabling an electrical parameter tobe determined from which it is possible to deduce the characteristicthat is representative of said reservoir.

[0013] In this way, it is possible for the support merely to house meansfor determining the potential differencl between said measurementelectrodes and a reference electrode, preferably situated on thesurface, in order to be able to deduce the resistivity of the formationssurrounding the reservoir and consequently the position of the contactsurface between the hydrocarbons and water, and thus be able to optimizeproduction.

[0014] In another embodiment, the support has an axial recess extendingover the full length of said support, said recess being designed toreceive the connection means.

[0015] This makes it possible in particular to avoid forming a leakagepath for fluids coming from the formation and the reservoir and goingtowards the surface by following the path of the wire connection alongthe casing, as can happen in prior art devices. In addition, by matchingthe shape of the connection means accurately to that of the axialrecess, and by a judicious selection of the material used, it ispossible to obtain sealing that is entirely satisfactory in terms ofpreventing any fluid from moving along said connection means.

[0016] Advantageously, the support also includes a recess for receivingmeans for positioning said support in the well.

[0017] In this manner, all of the elements that are to be mounted oncasing in the prior art can be positioned in recesses formed in thejacket of the support of the invention, thereby making it easier tolower the support down the well and ensuring that it can be cementedreliably when cement is injected between the walls of the support and ofthe well.

[0018] In an advantageous embodiment of the invention, the jacketsurrounding the cylindrical tube comprises:

[0019] a first layer of substantially constant thickness covering thewalls of the cylindrical tube; and

[0020] a second layer covering said first layer, and having the recessesformed therein, the thickness of said second layer being such that theoutside shape of the support is substantially cylindrical.

[0021] This embodiment makes it possible to adapt the thickness of thesecond layer locally so that regardless of the dimensions of theelements that are housed therein the support has no projections on itsoutside surface, thereby avoiding any impacts on said elements and anydefects in the cemented annulus.

[0022] The invention also provides a measurement device for monitoringand/or studying a fluid reservoir through which at least one wellpasses, said device comprising:

[0023] power supply and measurement processing means;

[0024] means for measuring a characteristic representative of saidreservoir; and

[0025] connection means connecting said measurement means to said powersupply and measurement processing means.

[0026] According to the invention, the device further comprises at leastone support, with said measurement means and said connection means beinghoused in the recesses in the jacket of said support.

[0027] Other advantages and characteristics of the invention appear inthe following description, given with reference to the accompanyingdrawings, in which:

[0028]FIG. 1 is a view of an embodiment of a support of the invention;

[0029]FIG. 2 is a diagrammatic view of an embodiment of a measurementdevice constituting an embodiment of the invention; and

[0030]FIG. 3 is a diagram showing an example of an application of theFIG. 2 measurement device.

[0031]FIG. 4 is a view of another embodiment of the support of theinvention.

[0032] As shown in FIG. 1, the support 1 of the invention issubstantially cylindrical in shape, comprising a tube 2 having a firstend 2 a carrying a male threaded portion and a second end 2 b carrying afemale threaded portion. The tube 2 is advantageously made of metal. Bymeans of these threaded ends, the support 1 can be associated with othersupports that are identical or with any other tubular structure so as tomake up a succession of segments of an overall duct. The support 1 alsocomprises a jacket 3 covering substantially all of the tube 2, exceptfor its threaded male connection end. In another embodiment, the support1 can be associated with other structures by being welded thereto.

[0033] As described below with reference to FIG. 3, the support of theinvention is intended specifically to constitute a segment of casingcovering the wall of a well passing through geological formations. Thenumber of segments constituting said casing thus depends on the lengthof the well, said segments optionally all being constituted by supportsof the invention or only a small number of them being constituted bysuch supports, with the other tubular segments having no jackets and norecesses. Where appropriate, the annulus between the casing formed inthis way and the walls of the well is subsequently cemented so as toconsolidate the assembly and isolate said casing from the fluids flowingin the terrestrial formations. In another application of the support ofthe invention, the assembly comprising at least one support 1 and aplurality of other segments constitutes part of production tubing,lowered inside casing covering the walls of a well (itself optionallyincluding at least one support of the invention) and conveying a flow ofeffluent coming from a fluid reservoir through which the well passes.

[0034] In the example shown in FIG. 1, the jacket 3 comprises at leastone, and advantageously a plurality of annular and/or axial recesses 4.The axial recess(es) 5 extend along the entire length of the support 1.These recesses can be covered in an optionally continuous sealing layerso as to further reduce the risk of fluid infiltrating between saidaxial recess and the wire connection that is to be installed therein. Inthis example, the recesses 4 are annular, however in general terms thejacket 3 has recesses of arbitrary shape given that said shapes need tocorrespond to the shapes of the measurement means, positioning means,etc. that are to be engaged in this way in said jacket. As explained ingreater detail with reference to FIG. 2, the purpose of the jacket 3 isto receive various measurement means or electrical, electronic, optical,or hydraulic connection means so that said means are fully includedwithin the thickness of said jacket and therefore do not stand proud,being no more than flush relative to the overall outside diameter of thesupport of the invention. Over the cylindrical surface of the support 1as a whole, the depth of the recesses 4 or 5 can therefore vary locallyas a function of the dimensions of the elements they are to receive, theessential point being that all of these elements are received fullywithin the thickness of the jacket 3.

[0035] In an embodiment, the jacket 3 is constituted by two layers ofdifferent materials: a first layer of constant thickness covering thewalls of the cylindrical tube 2, and a second layer of varying thicknessin which the recesses are formed. The function of this second layer is,so to speak, to “equalize” the outside profile of the jacket 3 so thatits outside diameter remains constant over the entire length of thesupport 1. The thickness of this second layer is thus a function of thedepth of the recesses. In an embodiment, the two layers of the jacket 3can be eccentric so as to gain depth for the recesses and thus minimizethe overall diameter of the support 1, depending on the particularelements that are to be positioned in said support. In anotherembodiment, which is easy to implement, the jacket 3 is made as a singlelayer in which recesses of various depths have been formed. In thismanner, as mentioned above, while the support of the invention is beinglowered down a well bored through terrestrial formations, it is thedirectly-exposed jacket 3 which is subjected to any impacts andfriction, while the elements it carries remain protected. The jacket 3is substantially cylindrical, but it could be eccentric relative to theaxis of the cylindrical tube 2.

[0036] The mechanical properties of the jacket are advantageouslyselected so as to be capable of withstanding the weight of the elementsinstalled in the recesses, and also the forces transmitted by theinstallation equipment (suspension jaws, protection sleeves, clampingjaws) used on the support while it is being lowered down an oil well. Inthis context, it is important to provide means for preventing damage tothe jacket 3 not only while the support is connected via its threadedends 2 a and 2 b to other supports or other tubular structures, but alsowhile said support (or a succession of such supports) is being lowereddown a well passing through at least one fluid reservoir. Solutionsknown in the state of the art can then be used such as using protectionsleeves around the jacket 3 to prevent the teeth of the jaws ofinstalling tools biting into said jacket, or it is possible to makedirect use of jaws without teeth but provided with a covering thatprovides sufficient grip to enable the support 1 to be handled.

[0037] The mechanical properties of the jacket 3 can also be selected insuch a manner as to increase the overall strength of the support 1, inparticular its ability to withstand pressure, and this is particularlyuseful when the support of the invention is intended to constitute asegment of casing covering the walls of a well. The jacket 3 also needsto be mechanically strong when explosive charges are placed in thesupport 3 for the purpose of locally puncturing said support to enablehydrocarbons to flow in from the formation. Under such circumstances,the placing of measurement means and wire connection(s) in the supportneeds to be arranged so as to ensure that exploding charges does notdamage this equipment.

[0038] Advantageously, the electrical properties of the jacket aredetermined by the nature of the measurement that are to be performed.When the representative characteristic of the reservoir is theresistivity of the formations surrounding said reservoir, it is for thejacket, or at least the first layer of said jacket in the above-citedexample, to be of a material that is electrically insulating so as toavoid interfering with the measurement means to be positioned in thevarious recesses 4 and 5, and in particular so as to avoidshort-circuiting them.

[0039] Finally, the chemical properties of the jacket 3 must also beselected so as to enable it to withstand the corrosive medium in whichthe support 1 is to be installed, in particular down an oil well.Satisfactory results have been obtained for a jacket 3 made of compositematerial (e.g. mixture of glass and epoxy), but it is also possible toenvisage using other materials such as ceramic or various thermoplasticcoverings.

[0040]FIG. 2 shows a measurement device 10 of the invention comprisingat least one support 1 of the invention having its recesses fitted withvarious elements. In one embodiment, a fraction of the recesses 4 areprovided with annular measurement electrodes 6. The number of suchelectrodes is arbitrary and depends on the type of measurement and/orthe desired accuracy. Advantageously, these electrodes are constitutedby rings of electrically conductive material (when the desire is toperform measurements of the resistivity of the formations surroundingthe reservoir) selected so as to be compatible with the measurements tobe made and the fluids that are present. Nevertheless, the electrodes 6can be of any shape and of any suitable material. In particular, whenthe annulus between the device 10 and the walls of the well is notcemented, the electrodes 6 can be provided with flexible metal springsfor ensuring electrical contact with the walls of said well. This isparticularly advantageous when the annulus is filled with an oily mudthat is electrically non-conductive. The electrodes are installed in therecesses 4 prior to the support being lowered down the well, and, asmentioned above, the recesses 4 are of dimensions such as to ensure thatthe said electrodes are no more than flush relative to the outsidediameter of the jacket 3.

[0041] The measurement electrodes 6 are connected via at least one wireconnection 7 to means for powering and processing measurements, whichmeans are preferably situated on the surface. Electronic means forintermediate processing (not shown) can also be integrated in thesupport 1 and can perform initial treatment on the measurements prior tosending them to the surface. The wire connection is received in theaxial recess 5. The power supply means are current feeder means when itis desired to perform “electrical” measurements, but it is also possibleto use hydraulic, optical, etc, . . . feeder means as a function of thekinds of measurement performed by the means 6.

[0042] When the measurement device 10 comprises a plurality of supportsof the invention connected end to end, the axial recess 5 can beextended over the entire duct built up in this way. For this purpose, itis advantageous for the recesses 5 of the support to coincide once thesupports have been connected together so as to form a continuous axialrecess enabling the wire connection 7 to be extended to the surface. Itis also advantageous to provide annular recesses in the jacket 3suitable for receiving clamping and sealing means (not shown in theinterest of clarity) that hold the wire connection in the axial recess5. In this manner, while the device 10 is being lowered down a well,these clamping means prevent fluids from infiltrating between the jacket3 and the connection 7, which could damage the jacket and saidconnection, and which could disturb measurements.

[0043] In the embodiment shown in FIG. 2, the measurement electrodescomprise at least one electrode for injecting current into theformations surrounding the well, a current return electrode, and ameasurement electrode, while a reference electrode (not shown) ispreferably situated on the surface. In this manner, the device of theinvention makes it possible to determine an electrical parameter(corresponding to the potential difference between a measurementelectrode and the reference electrode) from which it is possible todeduce the resistivity of the geological formations surrounding thewell, which resistivity decreases with increasing conductive fluidcontent in the formations, i.e. with increasing water content to thedetriment of hydrocarbon content. It should be observed that otherarrangement of current electrodes are possible, providing electriccurrent flows in the formation. Thus, the measurement device 10 can beused to implement a measureming and monitoring method of the kinddescribed in patent FR 2 712 627, the content of which is incorporatedherein by reference.

[0044] The device 10 can also be fitted with auxiliary devices likewisereceived in recesses specially provided in the support 1 of theinvention. Such devices can include in particular centralizers 9 asshown diagrammatically in FIG. 2 and known in the state of the art.Under such circumstances, the centralizers have portions that projectfrom the jacket 3 so as to ensure that the device is properly positionedin a well. This is particularly advantageous when cement is injectedinto the annulus between the walls of the well and said device, afterthe device has been put into place. Centralizers serve to ensure thatthe cemented annulus is of more uniform thickness, thereby minimizingweak points in the annulus. The support 1 for the device 10 of theinvention can also possess recesses fitted with pressure and temperaturesensors or sensors for any other parameter it is useful to know whenmonitoring and operating the reservoir through which the well extends.

[0045] When the device of the invention is fixed permanently down awell, its technical characteristics become particularly pertinent. Asalready mentioned, the fact that the outside profile of the device isuniform, i.e. free from any projections other than the centralizers,ensures not only that the various measurement means are protected whilethe device is being lowered into the well, but also guarantees theintegrity of the cemented annulus.

[0046]FIG. 3 is a diagram showing how a measurement device of theinvention can be used. A well 11 is bored through terrestrial formations12 and passes through at least one fluid reservoir 13. Casing has beenlowered down the well 11 and the annulus 15 between said casing and thewalls of the well has been cemented. The casing comprises a successionof segments constituted by measurement devices 10 of the invention,interconnected end to end via the threaded ends 2 a and 2 b of eachsupport 1. At least one of the devices 10 has measurement electrodes 6,and each of the devices 10 has a recess for receiving a wire connection7 taking the data picked up by the electrodes to means for processingthe measurements and for supplying power, which means 16 are situated onthe surface. This makes it simple to implement a method of monitoringand measuring data characteristic of the formations surrounding thewell, as described in patent FR 2 712 627, while preserving themeasurement means which remain permanently down the well and which it istherefore important to avoid damaging, and while also preserving theintegrity of the cemented annulus 15 so as to prevent infiltration offluid from the reservoir 13 or from formations between said annulus andthe casing.

[0047]FIG. 4 represents another implementation of the support accordingto the invention. A well 11 is bored through geological formations 12and passes through at least one reservoir 13. A casing has been loweredin said well. The annulus between a first part of said casing and thewalls of the well has been cemented until some liner hangers 14 thatisolate a last part of the casing from the first cemented part. Thislast part of the casing is made of several supports according to theinvention.

[0048] In one example of realization, the annulus between said last partand the wall of the well has been filled by gravel packs. For each ofthose supports, the cylindrical tube 2 comprises at least twosandscreens 17 between which the jacket 3 has been installed. Thisjacket comprises at least one annular recess, not visible on the figure,wherein one annular electrode has been installed. The measurement of theresistivity of the geological formations surrounding the borehole isthus realized through the plurality of annular electrodes each of thosebeing embedded in the annular recess of corresponding support, installedbetween corresponding sandscreens.

1/ A support for measurement means to be permanently installed in a wellin order to monitor and/or study a fluid reservoir (13) through whichsaid well (11) passes, said support comprising: a cylindrical tube (2);and a jacket (3) surrounding said cylindrical tube, the support beingcharacterized in that said jacket (3) has at least one recess (4, 5) forreceiving means (6) for measuring the resistivity of the geologicalformations surrounding said reservoir and/or connection means (7)leading to power supply and measurement-processing means (16). 2/ Asupport according to claim 1, characterized in the jacket (3) is made ofelectrically insulating material. 3/ A support according to claim 2,characterized in that it comprises a plurality of recesses (4) that areregularly spaced apart and designed to receive respectively measurementmeans (6) of electrically conductive material. 4/ A support according toclaim 3, characterized in that the measurement means (6) comprise atleast one measurement electrode, an electrode for injecting current intothe reservoir (13), and/or a current return electrode, enabling anelectrical parameter to be determined from which it is possible todeduce the resistivity of the geological formations surrounding saidreservoir. 5/ A support according to any one of claims 1 to 4,characterized in that it includes an axial recess (5) extending over theentire length of said support (1), said recess being for receiving theconnection means (7). 6/ A support according to any preceding claim,characterized in that it further includes a recess for receivingpositioning means (9) for positioning said support (1) inside the well.7/ A support according to any preceding claim, characterized in that thejacket (3) surrounding the cylindrical tube (2) comprises: a first layerof substantially constant thickness covering the walls of thecylindrical tube (2); and a second layer covering said first layer, andhaving the recesses (4, 5) formed therein, the thickness of said secondlayer being such that the outside shape of the support (1) issubstantially cylindrical. 8/ A support according to claim 7,characterized in that the first layer is made of electrically insulatingmaterial. 9/ A support according to any preceding claim, characterizedin that the ends (2 a, 2 b) of the cylindrical tube (2) compriseconnection means for connecting said support (1) to a second cylindricaltube and/or to a second support according to any preceding claim. 10/ Asupport according to any preceding claim, characterized in that thejacket (3) is substantially cylindrical and is eccentric relative to theaxis of the cylindrical tube (2). 11/ A support according to any one ofpreceding claims, characterized in that the cylindrical tube (2)comprises at least two sandscreens (17) surrounding the jacket (3). 12/A measurement device for monitoring and/or studying a fluid reservoir(13) through which at least one well (11) passes, said devicecomprising: electrical power supply and measurement processing means(16); means (6) for measuring the resistivity of the geologicalformations surrounding said reservoir; and connection means (7)connecting said measurement means (6) to said electrical power supplyand measurement processing means (16), said device (10) beingcharacterized in that it further comprises at least one support (1)according to any preceding claim, with said measurement means (6) andsaid connection means (7) being housed in the recesses (4, 5) in thejacket (3) of said support. 13/ A device according to claim 12,characterized in that it is permanently installed in the well (11) bycement (15) injected between said device (10) and the walls of saidwell.